This invention relates generally to the manufacture of generator stators and, specifically, to a device for measuring the radial distance between a radial stator core slot dovetail and the surface of the top or radially innermost armature bar in the stator core slot.
Armature bars are typically installed in radial slots formed in the stator core of the generator. The armature bars are supported by wedges slidably received in dovetail grooves formed in the side walls of the radial core slots.
More specifically, the current procedure for installing an armature slot-support system consists of several steps. One or more filler strips are installed on the surface of the top or radially innermost armature bar to fill the major portion of the radial clearance between the armature bar and the slot dovetail. A corrugated resilient spring is installed on top of the filler. A tapered dovetail wedge is then installed in the slot dovetail above the resilient spring. A second tapered wedge slide having a pre-defined interference fit relative to the dovetail wedge and the slot contents below is positioned for installation. The slide is then forced between the dovetail wedge and the resilient spring until the end of the slide is flush with the end of the wedge. The radial pressure that is developed as the slide is forced in should be sufficient to flatten the spring, seat the dovetail wedge against the slot dovetail, and compress the slot contents against the bottom of the stator core slot. Currently, to obtain the pre-defined interference fit, and, therefore, optimum wedging pressure, each slide is individually gauged by hand to determine the correct thickness, and then individually cut to length outside of the stator core. The process of correctly sizing and cutting each slide by hand is time-consuming, prone to error, and highly dependent on operator conformance to established gauging procedures. An incorrectly gauged slide can result in rework if the interference fit is too great or insufficient radial pressure if the fit is too small. A radially tight armature slot support system is essential for the long-term, reliable prevention of armature bar vibration that can result in premature failure of the armature winding.
This invention provides a device that applies a radial force to the stator core slot contents in two diametrically opposite stator slots, and simultaneously measures the radial distance between the slot dovetail and the surface of the top or radially innermost armature bar automatically and continuously along the entire length of the two slots. The acquired radial clearance information is processed and stored digitally and can be used to fabricate armature slot support parts with auxiliary tools to achieve a consistently tight armature slot support system.
The device, in accordance with the exemplary embodiment, includes a pair of drive heads connected by an expandable strut. The drive heads are engageable with armature bars in diametrically opposed radial stator core slots, and the expandable strut may be adjusted in length, as necessary, by a pneumatic cylinder or other appropriate device.
Each drive head includes a housing that mounts a plurality of axially aligned thrust wheels and a drive pulley. A drive belt extends about the thrust wheels and drive pulley, with the thrust wheels and driving portion of the belt adapted to fit within the stator slot and engage the armature bar surface. The drive pulley is actuated or driven by a motor, e.g., a servo motor, the output shaft of which carries the drive pulley.
Each drive head also includes a pair of distance measuring devices mounted forwardly and rearwardly of the thrust wheels and drive belt. Each measuring device includes a sensor module supporting a plate having tapered ends and adapted to slide within the dovetail grooves in the side walls of the radial stator core slot (also simply referred to as the xe2x80x9cslot dovetail.xe2x80x9d A spring-loaded plunger extends radially from the plate and is adapted to contact the surface of the top armature bar in the stator core slot. As the device is driven through the stator bore, with the drive heads traveling along the opposed radial core slots, the spring-loaded plungers will move radially in and out as the distance between the dovetail grooves and the bar varies. A linear voltage displacement transducer or LVDT associated with each sensor module detects the movement of the respective plunger and thus measures the distance between the slot dovetail and the surface of the armature bar. The data is then transferred to a microprocessor that also controls the axial movement of the device, where it is correlated with information relating to the axial position of the device along the stator bore.
The profile of radial distance from the slot dovetail to the surface of the armature bar versus axial location along the stator core slot is digitally stored for later use with auxiliary tools for fabricating armature slot support parts.
This process is repeated until a radial distancing profile is recorded for each armature core slot in the generator.
Accordingly, in one aspect, the invention relates to an armature slot radial clearance measurement device comprising a pair of opposed drive heads, connected by an expandable strut, each drive head fitted with a radial distance measurement device including a plate adapted to slide within a dovetail in a radial stator slot, spring-loaded plunger adapted to engage a surface of an armature bar located in the radial stator slot, and a transducer for detecting movement between the spring-loaded plunger and the plate.
In another aspect, the invention relates to a radial clearance measurement device comprising a pair of opposed drive heads connected by an adjustable strut, each drive head having supporting means for measuring radial clearance between dovetail grooves in a pair of diametrically opposed radial stator core slots and radially innermost armature bars seated in the stator core slots; and means for driving the device axially along the stator core slots.